feat: Tauri backend commands + wikipedia rewrite + github PR review pack

GUI integration
  - crates/jarvis-gui/src/tauri_commands/backends.rs — 5 new Tauri commands:
      get_active_backends()  -> {tts, llm, llm_model, profile}
      set_llm_backend(name)  -> swap LLM hot, persists to DB
      set_tts_backend(name)  -> persist choice (effective on jarvis-app restart)
      llm_reset_context()    -> clear conversation history
      llm_get_last_reply()   -> last assistant message or null
  - Registered in main.rs invoke_handler. Svelte side can now read active
    backend + swap from a settings page / footer without env-var gymnastics.

Wikipedia pack rewritten (resources/commands/wikipedia/)
  - Old `wiki/wiki.lua` (104 lines, hand-rolled Groq HTTP + inline SAPI PS) deleted.
  - Replacement `wikipedia/summary.lua` (87 lines):
    * REST summary endpoint (cleaner than opensearch+summary chain).
    * Russian first, English fallback with LLM translation.
    * Pure LLM fallback if Wikipedia has no article.
    * Uses jarvis.cmd.{ok,error,not_found} + jarvis.llm + jarvis.speak (no
      inline PowerShell SAPI). Phrases kept compatible with old pack.

GitHub PR voice review (resources/commands/github_pr/, 3 commands)
  - "текущий репо bossiara13/J.A.R.V.I.S-rust"  → github.set_repo
    Persists repo via jarvis.memory.
  - "какие пиары" / "открытые пиары"            → github.list_prs
    Calls `gh pr list --json number,title,author,createdAt --limit 10`.
    Parses count + first 3 titles by regex from JSON.
  - "разбери последний пиар" / "что в pr"       → github.summarize_pr
    `gh pr view N --json title,body,additions,deletions,changedFiles,author`,
    sends to LLM with "senior reviewer" system prompt, speaks 3-5 sentence
    review focusing on changes, risks, merge-readiness.
  - Requires gh CLI installed and `gh auth login` done.

Tests: 52/52 jarvis-core unit tests pass (Wikipedia pack TOML/script auto-checked).
Build: cargo build --release -p jarvis-app -p jarvis-gui green.

resources/commands/wikipedia/command.toml

@@ -0,0 +1,40 @@
+# Wikipedia summary — fetch a topic's intro from Wikipedia REST API, speak it.
+
+[[commands]]
+id = "wikipedia.summary"
+type = "lua"
+script = "summary.lua"
+sandbox = "full"
+timeout = 15000
+
+[commands.phrases]
+ru = [
+    "что такое",
+    "кто такой",
+    "кто такая",
+    "расскажи про",
+    "википедия",
+    "найди в википедии",
+    "что говорит википедия",
+    "поищи в википедии",
+    "википедия о",
+    "википедия про",
+    "найди в википедии про",
+    "статья из википедии",
+]
+en = [
+    "wikipedia",
+    "look up in wikipedia",
+    "wikipedia article on",
+    "what is",
+    "who is",
+    "tell me about",
+    "wikipedia about",
+]
+ua = [
+    "вікіпедія",
+    "знайди у вікіпедії",
+    "що таке",
+    "хто такий",
+    "розкажи про",
+]